The present invention is directed toward a fluid metering system and more particularly to a system which provides data indicative of the speed of sound energy propagation through the flowing medium as well as the flow characteristics of the medium.
Systems utilizing ultrasonic transducers in communication with a flowing medium are old in the art. Many systems have been disclosed which measure flow velocity, sound propagation velocity or both. Generally these systems require a voltage controlled oscillator for each direction of transmission through the flowing medium to provide an upstream and downstream frequency proportional to the speed of sound. Some systems employ switching means whereby one VCO may be made to serve for transmission in two directions. Other systems impose a quadrature between the received signal and the transmitted signal and control the output of a VCO through a phase detector. Other methods use the flowing medium as the frequency determinative element in an oscillating or "ring around" system.
Problems commonly arising in the foregoing types of metering systems relate to the loss of low flow rate information when using two oscillators, or the requirement for more than one pair of transducers when seeking to transmit upstream and downstream, or the necessity for unwieldy switching means, or any combination of these.